The present invention relates to primer compositions that may be mixed with water and water-based adhesives to provide a range of primers and priming adhesive compositions for bond improvement between polymers of similar or dissimilar types. More particularly the present invention relates primarily to water-based dispersions of surface modifying components for enhancing bond formation between substrates, such as polyolefins, which are known for low interfacial bond strength. Priming adhesives of the present invention improve adhesive bonding between materials without the application of surface pre-treatments.
Adhesives provide a relatively rapid and convenient way for attaching one type of material to another. Over the years, development of adhesive systems has addressed ways to modify the strength of the adhesive bond between selected materials. Depending on the application, the adhesive of choice may include a pressure sensitive adhesive, a structural adhesive, a hot-melt adhesive or a repositionable adhesive. Regardless of the wide range of available adhesives, the surfaces of some commonly occurring polymer substrates still lack suitable adhesive affinity to form strong bonds with other materials, whether similar or dissimilar. Lack of bonding to surfaces with low adhesive affinity also affects the bonding and retention of surface coatings or printing inks that may be used for surface marking or decoration.
One solution to poor bond formation and poor retention of coatings and inks lies in the use of special treatments to change the condition of a surface by increasing its surface energy. Surface treatments for increased surface energy include oxidizing pretreatments or the use of adhesion promoters. Oxidizing pre-treatments include the use of flame, ultraviolet radiation, corona discharge, and chemical oxidizing agents and the like. Adhesion promoters include chemical compositions containing e.g. solutions of styrene-ethylene/butylene-styrene block copolymers or acrylate polymers in an organic solvent. These compositions improve the bonding of pressure sensitive adhesives and structural adhesives to polymer substrates.
Unfortunately, these methods for raising surface energy are not without problem. For example, chemical oxidizing agents are typically hazardous materials requiring special handling. Surface treatment using flame, corona discharge, etc. usually requires special equipment of a design more suited to sheet or film or web processing than to surface treatment of shaped articles.
Both oxidizing and adhesion promoter pre-treatments provide improvement in bond formation associated with low surface energy polymers such as polyethylene (PE), polypropylene (PP), ethylene-propylene-diene terpolymer (EPDM) and ethylene-alpha olefin copolymers. Substrates of this type may also include ethylene-vinyl acetate copolymers as representative of polymers that are substantially free from ethylenic unsaturation.
Polymeric substrates that have some degree of ethylenic unsaturation also benefit from the use of surface pre-treatments. It is known for example, that rubbers comprising styrene/butadiene copolymers (SBR) require treatment with chlorinating agents including solutions of halogen donors such as trichloroisocyanuric acid, and N,N-dichlorobenzenesulfonamide, for improved bonding with adhesive bonding agents. Such halogen donors may be incorporated into primers or adhesives separately. The effectiveness of treatment by chlorination appears somewhat limited to substrates having a high level of ethylenic unsaturation such as polybutadiene, polyisoprene, natural rubber, styrene-butadiene copolymers, polychloroprene and the like. Also the addition of halogen donors reduces the stability of some adhesives, including polyurethane adhesives.
Further improvement in bonding to numerous types of substrates may be possible by abrading the surface of a substrate even before applying any pre-treatment. Mechanical means for surface roughening then represents a preliminary step to surface pre-treatments. Regardless of their effectiveness, pre-treatments represent an additional step in the process of manufacturing a product. Additional process steps incur additional time and expense and thereby add undesirable cost to a final product.
The development of primer pre-treatments, primarily in solvent, has yielded some improvement in adhesive bonding to low energy surfaces. U.S. Pat. No. 6,008,286, for example, provides compositions comprising mixtures of hydrocarbon polymers, halogen-substituted hydrocarbon polymers and substituted aliphatic isocyanates which, coated from solvent, improve the bond between low energy substrates and adhesives, coatings, printing inks and the like. The benefits of this primer and related solvent based primer compositions may be diminished by the need to limit volatile organic compounds (VOC) to a level that avoids health hazards and prevents environmental contamination.
Solvent based or aqueous based thermosettable primers may be used, for bond improvement, without a flame or corona preliminary treatment. U.S. Pat. No. 6,001,469 describes primers and topcoats of this type used with e.g. thermoplastic polyolefins (TPO) and reaction injection molded polyurethane (RIM). These materials may be suitably cured on the substrate at temperatures in the region of 130xc2x0 C. for 30 minutes. Similarly WIPO publication WO 94/28077 describes aqueous-based compositions requiring heat treatment at 130xc2x0 C. for 40 minutes. It is known (see e.g. R. Ryntz in xe2x80x9cWaterborne, High Solids Powder Coatings Symposium,xe2x80x9d Univ. of Southern Mississippi 1995), that high temperature treatment may also affect the surface morphology of thermoplastic polyolefin polymers. Such changes may be beneficial in some cases, but in others the relatively high temperature for curing may be sufficiently close to the material melting point to produce substrate dimensional changes and associated problems.
Attempts to include primer compositions and/or adhesion promoter compositions with adhesive compositions, have met with limited success. According to an article in the Journal of Coating Technology, 65, No. 827 p. 21 (1993), it is known that chlorinated polyolefin primer compositions do not provide the same level of priming when included as an adhesive additive. Similarly, water based adhesive compositions and primers for polyolefins, described in U.S. Pat. No. 5,298,552, appear primarily useful for applications requiring bonding of polyolefin sheets to porous fibrous substrates such as water-absorbent paper board and similar paper pulp or wood fiber products. Also, in this case, the composition of the adhesive component of the formulations appears to have more impact on the bonding force developed between a polyolefin and absorbent substrate than the chlorinated polyolefin. It appears that common solvents, such as toluene, xylene etc. are unsuitable for use with compositions described in U.S. Pat. No. 5,298,552. Instead, the preferred solvent is relatively uncommon dodecyl benzene.
Known water based primer compositions derive their stability from the use of conventional surfactant materials to keep active components dispersed in the aqueous phase. The amount of surfactant requires careful control. Insufficient surfactant leads to instability and precipitation of the dispersed phase. Addition of too much surfactant produces a primer having poor adhesion to substrates that require priming. Good adhesion is essential to effective performance of priming compositions.
In view of the above described deficiencies associated with the use of known adhesive bonding agents, particularly the use of multiple treatments at substrate surfaces, the present invention has been developed to alleviate these drawbacks and provide further improvement and cost reduction. These enhancements and benefits are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
The present invention in its several disclosed embodiments alleviates the drawbacks described above with respect to water dispersed primers and priming adhesive compositions and incorporates several additionally beneficial features. Of particular interest is the provision of primer solutions suitable for mixing with water and aqueous based adhesive dispersions to provide water dispersed primers and priming adhesive compositions. Depending upon the application, the variation of dispersed primer relative to dispersed adhesive produces a range of compositions from those functioning essentially as primers to others that contribute properties of priming and placement of an adhesive on a treated surface. Water dispersed primers and priming adhesives, according to the present invention, allow substantial reduction in the use of solvents. Solvent removal provides the benefit of substantial elimination of volatile organic compound (VOC) emission during improved processing and bond formation between polymer substrates. Improved processing refers to the elimination of pre-treatments, such as flame and corona treatments, when using primers and priming adhesives according to the present invention.
More specifically the present invention provides a water dispersed primer composition comprising a solution of a halogenated hydrocarbon polymer in organic solvent and a dispersing agent added to the solution to form a fluid primer to be dispersed in water to provide the water dispersed primer composition. Organic solvents may be selected from cyclohexane, heptane, hexane, xylene, toluene, chlorotoluene, mixed hydrocarbon solvents and mixtures thereof.
The present invention further includes a water based priming adhesive composition comprising an adhesive dispersion of an adhesive polymer dispersed in water, and a primer mixed with the adhesive dispersion to form the priming adhesive. The primer comprises a solution of a halogenated hydrocarbon polymer in organic solvent selected from the group consisting of cyclohexane, heptane, hexane, xylene, toluene, chlorotoluene, mixed hydrocarbon solvents and mixtures thereof. A primer composition may optionally contain a particulate dispersing agent.
The beneficial effects described above apply generally to water dispersed primers, priming adhesives and related compositions. Specific compositions providing these benefits will be described in detail hereinbelow.
As required. detailed embodiments of the present invention are disclosed herein, however, it is to be understood that the disclosed embodiments are merely exemplary of the various and alternative forms of the invention. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention.
Water dispersed primers and priming adhesives, according to the present invention, may be produced by adding a solution of a primer, in organic solvent, to water, or to a water dispersed adhesive composition or to a solvent based adhesive. The resulting compositions improve adhesive bonding to surfaces known to have low affinity for adhesive bond formation. Adhesive bonding improves even in the absence of oxidizing pre-treatments and conventional adhesion promoters.
Commonly owned U.S. Pat. No. 6,008,286 provides solutions of surface priming compositions dissolved in organic solvents. These priming compositions improve bonding of e.g. adhesives, inks and other coatings to substrates including organic high polymers that can be synthetic or natural and typically include elastomeric materials.
The benefits of the previously discussed solutions of primers in organic solvent may be realized, according to the present invention, using primer compositions dispersed in water or aqueous adhesive dispersions. Combinations of differing quantities of primer solutions with water and water dispersed adhesives provide a range of compositions that either behave simply as surface primers or priming adhesives. Surfaces primed with these water-based dispersions participate in strong adhesive bond formation with similar and dissimilar substrates. Surface primers and priming adhesives may be applied by spraying, or brushing, or wiping, or any other conventional coating method, followed by drying, by evaporation, to produce a primed surface. The use of water dispersed primers and priming adhesives has been shown to eliminate the need for pre-treatment of substrate surfaces.
Substrates suitable for use with primers and priming adhesives according to the present invention include uniform polymeric sections, filled materials and foamed materials. They fall mainly into the two classes of ethylenically unsaturated materials and those containing little or no ethylenic unsaturation, as follows:
Substrates with ethylenic unsaturation include: polybutadiene, polyisoprene, styrene-butadiene copolymer, styrene-butadiene-styrene block copolymer.
Substrates with essentially no ethylenic unsaturation include ethylene-propylene-diene terpolymer (EPDM), styrene-ethylene-butylene-styrene block copolymer, ethylene-propylene rubber, butyl rubber, bromo-butyl rubber, ethylene-alpha olefin copolymer, polypropylene, polyethylene, polyethylene vinyl acetate, and synthetic leather and blends and mixtures thereof.
Water dispersed primer compositions contain active materials based upon halogenated hydrocarbon polymers dissolved in an organic solvent. A priming composition may also include non-halogenated hydrocarbon polymers as a blend with halogenated hydrocarbon polymers. Halogenated hydrocarbon polymers may also include functional groups such as sulfonate an groups, carboxylic acid anhydride groups, hydroxyl groups, epoxide groups, carboxylic acid ester groups, carboxylic acid amide groups, carboxylic acid groups and the like. Suitable halogenated hydrocarbon polymers include chlorinated polyethylene, chlorinated polypropylene, chlorosulfonated polyethylene, maleic anhydride modified chlorinated polyethylene and blends and reaction products thereof Preferred halogenated hydrocarbon polymers are chlorinated polypropylenes modified with maleic anhydride and available commercially as CP 343-1, available from Eastman Chemical Company, Kingsport Tenn., HARDLEN CY-9122P, available from Toyo Kasei Kogyo, Ltd., Osaka, Japan, and HYPALON CP-826, available from DuPont Dow Elastomers L.L.C., Wilmington Del.
Non-halogenated hydrocarbon polymers, suitable for blend formation with halogenated polymers, may also include functional groups such as: carboxylic acid anhydride groups; hydroxyl groups; epoxide groups; carboxylic acid ester groups; carboxylic acid amide groups; carboxylic acid groups and the like. Suitable polymers include styrene-ethylene/butylene-styrene triblock copolymers (e.g. KRATON G-1657 available from Shell Chemical Co., Houston Tex.), maleic anhydride modified styrene-ethylene/butylene-styrene triblock copolymers, maleic anhydride modified ethylene-propylene copolymers, maleic anhydride modified polypropylene, maleic anhydride modified ethylene vinyl acetate copolymers and ethylene/butylene copolymers having terminal hydroxy functionality. Preferred non-halogenated hydrocarbon, commercially available polymers include: KRATON FG-1901X; and HPVM 2203, both available from Shell Chemical Co., Houston Tex.; FUSABOND MC-190D, available from DuPont Canada Inc., Mississauga, Ontario, Canada; and an ethylene vinyl acetate copolymer containing 72% ethylene, available from Polysciences Inc., Warrington Pa.
Preferred primers and priming adhesives require addition of solutions of halogenated hydrocarbon polymers, and optionally their blends with non-halogenated hydrocarbon polymers, in organic solvent to water, water-dispersed adhesives and solution adhesives. Solvents used in the preparation of surface primer solutions include aliphatic hydrocarbons, aromatic hydrocarbons and halogenated derivatives thereof. Suitable solvents include cyclohexane, heptane, hexane, xylene, toluene, chlorotoluene and mixed hydrocarbon solvents, available from Shell Chemical Co., Houston Tex., as SHELL CYCLO SOL (R) 100 and SHELL CYCLO SOL (R) 150. Preferably, the organic solvent, for priming compositions, is a mixture including a weight ratio of from about 95:5 to about 5:95, more preferably from about 80:20 to about 20:80, and most preferably from about 60:40 to 40:60 of either cyclohexane or heptane combined with xylene or SHELL CYCLO SOL (R) 100 or SHELL CYCLO SOL (R) 150.
Solutions of halogenated hydrocarbon polymers, or their blends with non-halogenated hydrocarbon polymers in the solvent mixtures, have solids contents from about 0.5 wt. % to about 30 wt. %, preferably about 2.0 wt. % to about 15 wt. %. Solutions of this type may be added to water, water dispersed adhesives and solution adhesives to provide primers and priming adhesives according to the present invention. Preferably the solutions are dispersed in the dispersion medium using from about 0.1 wt. % to about 5.0 wt. % of a dispersing aid such as fumed silica. The ratio of a solution of primer to dispersion phase formulation may be from about 90:10 to about 10:90, preferably about 50:50 to about 15:85 and more preferably about 25:75 based on the weights of each material.
Dispersing agents provide stability to water based dispersions according to the present invention. Suitable dispersing agents include particulate materials and polymeric materials. Fumed silica is a preferred particulate dispersing agent. Examples of suitable formed silica include AEROSIL 200, AEROSIL 300, AEROSIL 380, AEROSIL R-812 and AEROSIL R-972, all available from Degussa Corp., Ridgefield N.J. Polymeric dispersing agents include polyurethane polymers and acrylate polymers. A preferred polyurethane polymer dispersant is DISPERCOLL U-54, available from Bayer Corp., Pittsburgh Pa. An example of preferred polyacrylate dispersions is HYCAR 2671, available from B.F. Goodrich Performance Materials, Cleveland Ohio.
Optional additives for solutions containing primer, as described above, include: silane coupling agents; biocides; fungicides; optical brighteners; antioxidants; silica; pigments; dyes and acid scavengers, such as epoxy resins. Such additives, used alone or in combination, preferably represent less than wt. % of the water dispersed formulations.
Fluid priming compositions of chlorinated hydrocarbon polymers, organic solvent, dispersing agent and optionally non-halogenated hydrocarbon polymers, when added with stirring to water produce water dispersed primers according to the present invention. Similar priming compositions, when added with stirring to water dispersed adhesives provide priming adhesive compositions according to the present invention. A comparable non-aqueous priming adhesive also forms upon addition of these priming compositions to solvent based adhesives.
Adhesives used for the preparation of priming adhesives include water dispersed adhesives and solvent-based or solution adhesives. Useful water dispersed adhesives include polyurethane latices and acrylate polymer latices and blends thereof. Suitable polyurethane latex adhesives comprise from about 35% to about 60% of polymer solids dispersed in water, including DISPERCOLL U-53, DISPERCOLL U-54 and BAYHYDROL DLN, all of which are available from Bayer Corp., Pittsburgh Pa. Acrylate latex adhesives, having from about 50% to about 65% of polymer solids in water, include HYCAR 2671, available from B.F. Goodrich Performance Materials, Cleveland Ohio., and RHOPLEX A-920, available from Rohm and Haas Chemical Company, Philadelphia Pa.
Solution adhesives, useful for the present invention, may be selected from a range of polyurethane adhesives containing from about 15 wt. % to about 30 wt. % solids dissolved in a solvent such as methyl ethyl ketone (MEK). Suitable commercially available polyurethane adhesives include DESMOCOLL 306, DESMOCOLL 530, DESMOCOLL KA8741, DESMOCOLL 620, DESMODUR CB-55N, and DESMODUR CB-72N, all available from Bayer Corp., Pittsburgh Pa.; PEARLSTICK 45-60/18, and PEARLSTICK 45-60/25, available from Aries Technologies Inc., Dervy N.H., and MORTHANE CA-100 series adhesives available from Rohm and Haas Inc., Philadelphia Pa.
For added hydrolytic stability and adhesive strength, polyurethane adhesives used herein may employ from about 3.0 wt. % to about 5.0 wt. %, of the total composition, of a polyfunctional isocyanate crosslinker. Suitable materials for use in solution adhesives include: DESMODUR RFE, available from Bayer Corp., Pittsburgh Pa.; and/or IRODUR E-321 available from Rohm and Haas Inc., Philadelphia Pa. Crosslinkers used with aqueous-based latex adhesives include: DESMODUR DA; DESMODUR KA; DESMODUR 8703, all available from Bayer Corp., Pittsburgh Pa. Catalysts such as dialkyl tin carboxylates, metal acetyl acetonates, metal carboxylates, mixtures of metal acetyl acetonates with tertiary amines and the like may be used to accelerate reaction between crosslinkers and adhesive polymers.